1. Technical Field
The present invention relates to a method of manufacturing a flange structure.
2. Description Of Related Art
Block anchors for use in parking brakes for vehicles, for instance, have flanges that greatly and elliptically overhang outward from outer circumferences of shafts. In manufacturing such component, the flange is often formed by hot forging because material is greatly deformed.
However, hot forging is disadvantageous, in that: the cost is increased (as hot forging requires a large-sized device); a manufacturing rate is low; skill and experience are required; additional processes such as cutting and grinding are required after forging for components requiring high dimension precision (as hot forging hardly results in final products with good surfaces); and the like.
Use of cold forging has been examined in all processes. However, such method is not practically applicable to a manufacturing of, for instance, a component that requires a greatly-overhanging flange because the pressure at the time of forming the component is excessively increased.
In addition, when the overhanging shape of the flange is non-circular (e.g., elliptic), the material is circularly overhung by swaging and subsequently subjected to cutting and burring to conform to the targeted shape of the flange. Thus, the material yield is reduced.
As one solution for the problem describe above, Japanese Patent No. 4920756 (hereinafter referred to as “Patent Document 1”) discloses a method of manufacturing a flange structure including two forging steps of a first and a second forging steps. In the first forging step, a product with a thicker head than a flange of an anchor block is formed. Then, in the subsequent second forging step, the head of the product formed in the first forging step is squeezed by a die and a punch with at least a part of an outer circumference of the head free from a constraint by the die and the punch. The resulting product has a brim portion one size greater than the flange. Thereafter, an excessive portion that protrudes outward from the brim portion is punched into a profile of the flange.
By performing the forging in two steps as described above, the brim portion is formed to have a profile close to the final profile of the flange in the second forging step. Therefore, the excessive portion to be cut off is small, which contributes to improve the material yield. In addition, when the head is squeezed in the second forging step, a part of the lateral surface thereof is not constrained by the die. Therefore, the excessive material is forced out as bur from between the punch and the die. Therefore, a compression load required for the forming at each step is small, obtaining the flange with a great overhanging area without use of hot forging.
According to Patent Document 1 described above, the targeted anchor block to be manufactured is a single-shaft anchor block with a shaft portion only at a single side (i.e., the shape represented by solid line in FIG. 24). However, the anchor block G includes a dual-shaft structure with a shaft portion at both sides (i.e., the structure including, in addition to the shaft portion 7 represented by solid line, a shaft portion 3 represented by two-dot chain line in FIG. 24). When the dual-shaft anchor block G is manufactured according to the method disclosed in Patent Document 1, as illustrated in FIGS. 25 and 26, a punch P for use in the second forging step may preliminarily have a shaft forming hole 500. Then, in the second forging step, the head H of the product mounted on a die hole 510 of a die D may be squeezed with the punch P to form the brim portion I and the shaft portion 3 at the same time. However, according to Patent Document 1, in order to make the compression load at the time of forming small, a part of the lateral surface is not constrained by the die when the head H is squeezed. Thus, even when an attempt is made to squeeze the head H and to form the shaft portion 3 at the same time, most of the material may flow outward, and thus the shaft portion 3 will be difficult to be formed.